1. Field of the Invention
This invention relates to a polarization conversion system that converts unpolarized light to a specifically polarized light, and to an optical system using the polarization conversion system.
2. Description of the Related Art
Liquid crystal panels are extensively utilized in direct-view display apparatuses and projectors. In a projector, for example, liquid crystal panels (liquid crystal light valves) are used to modulate illumination light in accordance with image information, and the modulated light is projected onto a screen to thereby display images. Generally, since the images are displayed by modulating specific linearly polarized light, it is necessary to provide a polarization plate at the light entry side of the liquid crystal panel in order to convert the unpolarized light emitted by a light source to the requisite linearly polarized light. However, this results in the loss of half or more of the light due to absorption by the polarization plate. To increase the light utilization efficiency of the illumination system with respect to the liquid crystal panel, an optical polarization conversion system is typically employed to convert the light from the light source to one type of linearly polarized light.
Japanese Patent Laid-open Gazette No. 8-304739 discloses an illumination system using a polarization conversion system. This polarization conversion system comprises a polarization splitting prism array consisting of a plurality of polarization beam splitters and a plurality of reflecting mirrors, and a .lambda./2 retardation film provided on the exit side of the polarization beam splitting prism array. In this polarization conversion system, the polarization splitting prism array is used to split the unpolarized light into two types of linearly polarized light in which the plane of polarization of one is perpendicular to that of the other, and a .lambda./2 retardation film is then used to align the polarization direction of one of these beams of linearly polarized light with the polarization direction of the other beam of linearly polarized light, whereby the light is converted into substantially one type of linearly polarized light.
The problem with the polarization conversion system of the prior art is the need to use a complex polarization splitting prism array including multiple polarization beam splitters and reflecting mirrors in order to effect the conversion of the unpolarized light to the two types of linearly polarized light.